Evidence of a Order-Disorder Transition in the Crystalline Phase of Cd 6 Yb, 1/1 cubic approximant of icosahedral Cd 5.7
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S8.16.1
Evidence of a Order-Disorder Transition in the Crystalline Phase of Cd6Yb, 1/1 cubic approximant of icosahedral Cd 5.7 Yb N. Sorloaica, A. L. Pope, D. W. Winkler and Terry M. Tritt* Department of Physics and Astronomy, Clemson University, Clemson, SC 29634 USA
V. Keppens Department of Physics, University of Mississippi, Oxford MS
D. Mandrus and B. Sales Novel Materials Group, Solid State Division Oak Ridge National Laboratory, Oak Ridge, TN
Abstract The electrical and thermal transport properties (electrical resistivity, thermopower, heat capacity and thermal conductivity) of the crystalline phase of the binary Cd6Yb system has been measured over a temperature range from 10 K to 300 K. Evidence for a phase transition in Cd6Yb is observed in the electrical transport properties with distinct changes in the temperature dependence of the resistivity and thermopower around T ≈ 110K. An anomaly in the heat capacity and a thermal conductivity is also observed at this same temperature. Hysteretic behavior is not evident in the temperature dependence of any of the electrical and thermal transport properties.
In addition, the elastic properties using resonant ultrasound (RUS)
techniques have been investigated over a similar temperature range. A large “resonance dip” is observed in the RUS data at T ≈ 110K, which is indicative of some type of structural change in the crystalline material at this temperature. These data will be presented and discussed in context of the undergoes reversible order-disorder transition in the 1/1 cubic approximant at about 110 K, which makes the system very interesting compared to the quasicrystal phase Cd5.7Yb
S8.16.2
Introduction
Recently the Cd-Yb system has been of interest due to the discovery of a stable binary quasicrystal in this system, which exists in a narrow region of the phase diagram with a composition, Cd5.7Yb. [1][2] In an effort to more fully understand the novel transport in the quasicrystalline phase several samples of the crystalline Cd6Yb, were synthesized and measured for comparison. The Cd6Yb material is a cubic phase of the Yb-Cd system, with space group Im3, lattice parameter a = 1.564 nm and it consists of 168 atoms. The stoichiometry of the crystalline approximant Cd6Yb is very close to those reported for the quasicrystalline material and also the calculated diffraction patterns of Cd6Yb crystal agree very well with those observed by single-crystal X-ray diffraction of the icosahedral Cd5.7Yb quasicrystal. [1] [2] A series of electrical resistivity, thermopower, heat capacity and resonant ultrasound (RUS) measurements were performed on several samples of Cd6Yb. From these measurements, evidence is presented for a structural phase transition in the crystalline Cd6Yb system at T ≈ 110K, which is discussed in this paper.
Experimental Procedure
The alloy of Cd6Yb was prepared with stoichiometric amounts of Yb (3N) and Cd (5N) melted for 1h at 700˚ C and furnace-cooled to room temperature. Six samples of the crystalline Cd6Yb material were synthesized and m
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